Generation of a sine wave



July 3, 195 A. J. BARACKET GENERATION OF SINE WAVES CIRCUIT UTILIZATION Filed Jan. 29, 1949 SIGNAL SOURCE Fig. 2

Fig. 3

Fig. 4

7 H H H r Fig. 6

Patented July 3, 1951 GENERATION OF A-SINEJ WAVE Albert. J. Baracket,;Bloomfield-, N. J., assignor to- Allenv B. Du .Mont Laboratories, Inc.,-.Passaic, N. J a corporation of Delaware Application January29, 1949, Serial-No. 73,650

1 Claim. 1

My invention relates to electronic signal voltage generating circuits and more particularly to means for derivin a sinusoidal voltage Wave from an impulse type voltage wave.

In many electronic systems such as television, it is desirable to generate in a particular part of the system a sinusoidal voltage wave havin its frequency determined by a signal or recurring pulses while the amplitude thereof is independent of the amplitude. or shape of the pulses. Aften, it is desired that the sine wave have a frequency which is an harmonic of the signal pulses. In systems such as television that signal is complex having a varying wave form between pulses. In each instance a desired sine wave voltage must be obtained from the available signal.

..It is well known that a square wave voltage has a. greater amount of electrical energy in its fundamental sine Wave component than has a narrower pulse type Wave of the same frequency and amplitude.

Accordingly it is one object of this invention to generate a sinusoidal voltage having a frequency determined by that of'a recurring nonsinusoidalsignal.

Another object is to generate a sinusoidal voltage having a frequency equal to an integral multiple of the frequency of a recurring impulse component in a synchronizing signal.

Other objects will. be apparent after a study of the specification and drawings in which:

Figure 1 is a circuit diagram of an oscillator in accordance with one embodiment of the invention;

Figure 2 shows the wave form of a typical'television synchronizing voltage ;v

Figure 3 shows a typical voltage wave form generated by the oscillator shown in Figure I;

Figure 4 shows the desired sinusoidal voltage output from the oscillator of Figure 1; and

Figures 5 and-6 show voltage. wave forms corresponding to those shown in Figures 3 and 4, respectively, when it is desired to obtain the second harmonic of the synchronizing voltage.

Referring inmore detail toFigure 1, it may be seen that a source Ill of signals which may be, for instance, apreceding amplifier stage in. a television transmitter or other television circuit is connected to an input grid H of a thermionic tube Id. The anode [3' of the tube It is connected through a suitable resistor l5 to a source I6 of positive potential for operation thereof and also through a coupling capacitor l! to the grid 20 of a second thermionic tube 23. The cathode l2 of the tube I4 is connected through a resistor l9'toxground. The cathodezi of thesecond-tube 23 is also connected to ground through thisisame resistor I9. Thetinput gridzll-of the second tube- 23- is' connected to the cathode lead through: a

suitable resistor 3' which as may be seen is in series: with the resistor l9' to ground; This'resistor" lB -may be made variable as desired: for varying the time constant of the circuit as? well understood by those' skilled in the art.

The anode 22 of the second tube 231 isconnected through. a tuned circuit. 21-" to: a source 28' of positive potential. This latter source 28 of positive potential may be the same source as provided for operation of the first tube I4; if desired. The'tuned circuitZ'l preferably comprises a capacitance" 25:111 parallelwith an inductance 26. Additional plate load resistance-'24 may beconnected to the anode 22 of the tube 23 if desired to'increase' this plate resistanceforreasons which will hereinafter. be explained. in'connection: with the operation of the circuit.

A utilization circuit 29 which. may be the .de

siredztelevision circuit utilizing a sinusoidaliwave havinga frequencyawhich' is equal'to or a multiple of that of the television.synchronizingpulses, is

connected by a. suitable" leadriill to the anode 22' ofthet-ube 2.3? and the tuned circuit 21.

The-circuit thus described will be recognized asa form of multivibrator circuit known as a single-shot or single-acting multivibrator which requires a triggering impulse to fire'or change the state of operation of the circuit.

The operation of thecomplete circuit in Figure 1 is as-follows: At the start of the operation, vacuum tube 23 is drawing plate current from battery 23 through inductance 26. This current flows through resistor l9 to ground raising the voltage of cathodes l2 and 2! above ground by an amount equal to the voltage drop across resistance Hi. This voltage drop may be made high enough so that the grid H, which is normally at ground potential, is sufliciently negative with respect to cathode 1-2 toprevent tube Mfrom drawing plate current. Therefore, there will be no voltage drop across resistor I5; and

l3, illustrates the voltage drop due to plate current flowing through resistor by the sharp drop from level 66, which is the voltage of battery IE to level 61, which is the voltage between plate 13 and ground when vacuum tube l4 draws current.

Since the voltage across condenser 11 cannot change instantaneously, the voltage between grid and ground is suddenly reduced by a value equal to the voltage drop across resistor l5. As a result grid 20 is driven sufficiently negative with respect to cathode 2| to cut off the plate current through tube 2'3. By virtue of the inherent properties of inductance, the current through the inductance 26 immediately starts to charge condenser so that lead is raised from its former potential, which was essentially the potential of the battery 28. In Figure 4, which shows the voltage between lead 30 and ground, reference character 68 indicates the voltage of battery 28. As condenser 25 charges, the current through the inductance 26 decreases sinusoidally until the condenser is fully charged. At this time one fourth of the cycle of the sine wave has been completed as indicated by level 69 in Figure 4. When condenser 25 is fully charged, the current through inductance 26 ceases. Condenser 25 immediately starts discharging through inductance 26 with the result that current flows through inductance 26 in a direction opposite to or negative with respect to the original direction. This current increases negatively until condenser 25 is completely discharged as shown at point 10.

During the period that condenser 25 was charging and discharging, condenser l1 was discharging through resistors I5, l8 and IS. The time constant of condenser 11 and resistors I5, l8 and I9 is chosen in accordance with well known principles so that condenser I1 discharges to the point where vacuum tube 23 starts to draw plate current just as condenser 25 returns to its original, discharged condition. This plate current flows to ground through resistor 19 and acts, in the cumulative manner well known in the multivibrator art, to out 01f the plate current of vacuum tube [4 practically instantaneously.

The negative current through inductance 26 cannot stop instantly after discharging condenser 25 but must decrease gradually. As it decreases, it starts to charge condenser 25 in the negative direction and this action causes the current to die out in a sinusoidal fashion exactly as it did during the first quarter cycle. The plate resistance 24 is used to keep the positive plate current from discharging condenser 25 too rapidly and thus distorting the sinusoidal wave form, but it may be dispensed with if the plate resistance of vacuum tube 23 is sufficiently high. For this reason a pentode is sometimes used instead of triode 23 shown. By the time condenser 25 is fully discharged and the current through inductance 26 has reached its original value and direction, the cycle is finished and a new synchronizing signal applied to grid ll starts a new cycle. I

The square wave can insert energy into a tuned output or tank circuit during no more than half of each cycle of the tank oscillation. The same principle applies when the tank is tuned to a multiple of the fundamental frequency. As an example, when the tank is tuned to the second justed so that when the plate current of vacuum tube 23 is cut off, it will remain off while the tuned circuit of inductance 26 and capacitor 25 goes through one and one-half cycles. At the time the tuned circuit starts the second half of the second cycle as indicated by reference character H in Figure 6, vacuum tube '23 starts to conduct and supplies power to the tuned circuit until the next synchronizing pulse causes vacuum tube 23 to be cut off at the start of the third cycle of the timed circuit. If the synchronizing signal has the same fundamental frequency as before and it is desired to obtain the second harmonic of that frequency, the tuned circuit must, of course, be retuned either by changing inductance 26 or capacitance 25.

Typical values for the circuit of Figure 1 when used to transform 60 cycle pulses into a 60 cycle sine wave in a television camera control unit are illustrated in the drawing.

In the example given the plate resistance of vacuum tube 23 accomplishes the function of resistance 24 and resistor I8 has a predetermined fixed value.

While the particular circuit shown represents the preferred embodiment, it will be understood by those skilled in the art that modifications are possible without departing from the scope of the invention.

What is claimed is: 7 An electronic generator of a sinusoidal voltage of a predetermined frequency comprising a multivibrator of a single-acting type having a first and a second thermionic tube, a source of assymmetrical rectangular triggering impulses repeticonnected to a point between said tuned circuit and said first named resistor.

ALBERT J. BARACKET.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,395,368 Bull Feb. 19, 1946 2,423,304 Fitch July 1, 1947 2,426,996 Goodall Sept. 9, 1947 2,434,920 Grieg Jan. 27, 1948 2,436,808 Jacobsen Mar. 2, 1948 

